Caffeine does irritate the bladder I'm afraid. And if you are susecptable to water infections its best to give it a miss. I only drink de-caff tea now, I have it just like normal tea with milk etc and you really cannot taste the difference!
I found this on the internet:


Caffeine and alcohol

Cut down on tea, coffee, cola and other caffeinated drinks. Caffeine irritates your bladder and can make UUI worse.

Caffeine is also a diuretic, so for every cup of coffee you drink, you’ll pass a greater volume of water than that one cup. Cutting back on caffeine can help decrease the urgency and frequency of visits to the toilet.

Cut down on alcohol. It’s likely to worsen any type of urinary incontinence because it is a diuretic and stimulates the kidneys to produce more urine.

And as kayc said, cranberry capsules are great, I usually take 4 anytime I feel a sting coming on. (Suggested to me by a pharmacist some years ago, and I have never used anything else since!)